The invention relates to a system for transmitting a series of bits with an indefinite length by transmitting parts of the series in five-bit signals, the five-bit signals being protected by a conversion into six-bit signals, five of these six-bit signals together with two additional bits forming a balanced block.
Such a system is described in the Netherlands patent application No. 7,307,959, published Dec. 10, 1974.
The 32-bit block according to this known technique is composed e.g. as follows:
______________________________________ B1 t1 t2 t3 t4 t5 B2 ______________________________________ number of bits 1 6 6 6 6 6 1 ______________________________________
a first bit B1, which is information dependent. PA1 Five-bit signals t1 through t5 with a constant ratio of (3), (4) or (2) according to the said Netherlands patent application No. 7,307,959. PA1 a last bit B2, by which the block is balanced. PA1 a first bit x, which is information dependent. PA1 the signal .beta., characterizing the block as a framing block. PA1 a bit x, which is the inverse of the first bit. PA1 In the odd bit positions 9. 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, and 31 a binary representation is given of the channel number by the bits a to 1. The block would begin with this channel number, if it were a traffic information block. PA1 In the even bit positions 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 and 32 a binary representation of the same channel number is given in an inverted way by the bits a to 1.
The signals t1 through t5 have resulted from the conversion of 5-bit signals into 6-bit signals, as described in the said patent application. In this case there are in addition to the 32 informative signals, three further (3) signals available, viz. the signals .alpha., .beta., and .gamma.. Consequently, these signals do not occur in the transmission of the information.
As soon as a synchronization of the blocks, called framing in what follows, has come about, it will only get lost in case of interruptions of a certain minimum length. The constant ratio (see the above-mentioned patent application) no longer exists in case of loss of phase, which is quickly ascertained, and the problem is how to restore the framing again in a quick way.